Not Applicable
Not Applicable
Not Applicable
The present invention relates to direct current torque motors of the type intended for forward or reverse rotation by an amount less than one complete revolution of the motor rotor. Torque motors of this type typically are employed for servo actuator devices where fractional revolution rotation of a shaft is required for performing a work function. In particular, torque motors have found application for actuating the air intake throttle valve of an internal combustion engine for vehicular applications in response to a control signal provided by an electronic controller. This is due in part to the recently imposed strict engine exhaust emission requirements for motor vehicles which have necessitated electronic control of vehicle engine operating parameters.
In such internal combustion engine throttle applications and particularly engine throttle applications for motor vehicles, it is desired to minimize the size and weight of the torque motor in as much as it must be attached to the engine throttle body structure and is therefore subjected to the elevated temperature and vibration generated by the engine. In such engine throttle applications, the torque motor must provide a substantial torque output with minimum motor coil excitation current because the motor is operating, in a typical automotive application, at relatively low voltages on the order 12-24 volts DC. It has therefore been desired to provide an electrically operated motor vehicle engine throttle actuator to provide a torque motor which produces a maximum torque with a minimum of magnetic pole structure mass in the rotor and stator for a given coil excitation current. It has also been particularly desired to provide a torque motor for vehicle engine throttle applications which is robust and accurate in rotor positioning in order to correctly position the vehicle throttle in response to an electrical throttle control signal from an on board electrical controller. Furthermore, it has been desired to provide a low voltage direct current torque motor of minimum mass and size for a vehicle throttle application which does not require magnetic flux loop or pole structure fabrication of relatively exotic or expensive materials of high magnetic permeability but is capable of being fabricated from relatively low cost iron based material.
An example of a known engine throttle torque motor arrangement is that shown and described in U.S. Pat. No. 4,698,535 issued to Shiraki, et al. which utilizes a disc like rotor with axially oppositely disposed permanent ring magnets. The aforesaid known throttle torque motor is assembled over a shaft extending from a pre-assembled throttle valve body and has the disadvantage of being complex and difficult to assemble and calibrate. Known direct current torque motors for vehicle engine throttle operation have provided the requisite torque for insuring proper throttle positioning for a given control signal, however, the known torque motor designs have proven either prohibitive in production costs for high volume mass production vehicle applications, or have been prohibitively bulky and heavy, and have required difficult and complex assembly operations to install on the vehicle engine throttle valve and calibrate when installed.
Therefore, it has long been desired to provide a direct current torque motor for servo actuator operation at relatively low voltages, particularly for vehicle engine throttle positioning which has a minimum mass, volume and maximizes the torque output therefrom for a given motor coil excitation current and which is easy to assemble, install and calibrate.
It is an object of the present invention to provide a relatively low cost compact torque motor capable of operation at relatively low voltages and which provides maximum torque output for a fraction of a revolution of rotation of the motor shaft in forward or reverse direction and has a maximum power density with respect to the mass and volume of the motor for a given level of electrical energization. It is a further object of the present application to provide a torque motor particularly suited for use as a vehicle engine throttle actuator.
The present invention provides a torque motor having the magnetic flux loop including an axial air gap formed between stator coils and an annular rotor formed of ferrous material having permanently magnetized pole segments thereon. The magnetic components thereof, particularly the stator and rotor, are formed of low cost ferrous material such as low carbon steel with the stator disposed adjacent a disc-shaped rotor having permanent magnets disposed about the periphery and forming an axial air gap with the stator. The stator, stator coils, rotor and motor housing are pre-assembled over one end of the motor shaft and electrically calibrated as a unit or subassembly and then installed onto a vehicle throttle body with the shaft journalled on bearing surfaces provided therein and the throttle plate or member is subsequently assembled to the shaft. The pre-assembly of the motor to the shaft as a unit enables the motor to be electrically calibrated for rotational shaft movement prior to assembly into the vehicle throttle body thereby greatly simplifying assembly, calibration and testing and thus providing a relatively low cost torque motor for vehicle throttle applications.